Amplifier



G. H. PARIS Dec. 29, 193e( AMPLIFIER s sheets-sheet 1 Filed Feb. 20, 193D Dec. 29, 1936. Q H, PARlS 2,065,610

AMPLIFIER Filed Feb. 2o, 195o v-:s sheets-sheet 2 ankommt' Dec. 29, 1936. G. H. PARIS 2,065,610

AMPLIFIER Fi led Feb. 20. 1950 3 Sheets-Sheet 3 O 'S C P: n o

sv uucnnnnu Q l o I L I 1 w l I Q E 5o Q t 1 N .a I Q E I w E mi :h sgr/ty a: a 'o Nb ml S l1 no v v gwwntoz Patented Dec. 29, 1936 UNITED STATES PATENT @FFME AMPLIFIER Guy H. Paris, Duluth, Minn.

Application February 20, 1930, Serial No. 429,960

Claims.

This invention relates to circuits for radio receiving and thermionic amplifying apparatus.

The principal object of the invention is to provide a method of connecting elements of thermionic vacuum tubes to different points or voltage levels along a resistor or battery to obtain the proper operating voltages, such that the grid of each tube is at the same electrical potential as the plate of the preceding tube, and at the same time the plate of each tube is at the proper operating potential with respect to its filament, and the grid of each tube is at the proper potential with respect to its filament, thus permitting the plate of one tube to be connected direct to the grid of the following tube by a wire. This eliminates the use of transformers or condensers customarily used as a coupling means between tubes; and also eliminates bucking voltages sometimes used in circuits ywhere transformers or condensers are eliminated.

The invention particularly refers to a push pull amplier, although the principle can be equally well applied to a single sided circuit with correspondingly equal advantages, and it is not intended to limit the invention to a push pull amplier.

Another object of the invention is to provide a method of substantially blocking out or attenuating direct current voltage or slow voltage changes across the input of the amplier, preventing these direct current voltages or slow Voltage changes from progressing through the amplifier and being amplied through each succeeding stage, and at the same time permitting the comparatively fast varying signal voltages to progress through the amplifier and be amplied through each stage, thus providing a practical method whereby the detected signal can be applied direct to the input of an audio frequency amplifier eliminating the necessity of using condensers or transformers customarily used to prevent the direct current voltage component in the output of a detector or other input source from being impressed on the grids and progressing through the amplifier.

Another object of the invention is to permit a regenerative feed back to be applied in the amplifier wit-hout the necessity of using reactances to accomplish this purpose.

A construction accordance with the principal object of the invention results in its being possible to eliminate all reactance coupling ,otherwise necessary,-which forms another object of the invention.

With the foregoing and other equally important objects and advantages in View, the invention resides in the certain new and useful combination, construction, and arrangement of parts and circuits as will be hereinafter more fully described, set forth in the appended claims, and illustrated in the accompanying drawings, wherein:

Figure. 1 is a wiring diagram illustrating a two element rectifier coupled to a push pull circuit wherein the plate of one tube is connected by a wire to the grid of the succeeding tube:

Figure 2 is a diagrammatic illustration of a method of coupling, by means of a phase inverter tube, a grid bias detector to a push pull circuit wherein the plate of one tube is connected by a wire to the grid of the succeeding tube;V

also showing a method of obtaining regenerative feed back: both obtained without the use of the customary reactances:

Figure 3 shows diagrammatically a method of coupling a two element rectier to a push pull circuit wherein the plate ofA one tube is connected by a wire to the grid of the succeeding tube, and showing a method of obtaining regenerative feed back to the screen grid of the iour element tube.

Figure 4 is a diagrammatic representation of that portion of Figure l which acts to permit the rectied output of a two element detector to be applied direct to the push pull circuit by stabilizing the circuit against slow voltage changes.

The fundamental circuits illustrated in the several views are identical, but referring particularly to Figure 1, the voltagesupply source is indicated at i and may be a battery or any suitable rectier capable of supplying 724.6 volts which is the proper voltage for the circuits herein described. The voltage source l is connected by the wires 2 and 3 to the plate voltage supply resistor R, Rl, R2, R3, and R4, across which any voltage maybe obtained, up to an amount equal to the voltage of the supply source, and to the center tap of the output audio frequency choke coil I8.

Two screen grid 224 tubes 4 and 5 and two 250 tubes 6 and 'I are used in the circuit herein described, and the filaments of the tubes are heated by alternating current, the transformers being indicated at 8 and 9.

The signal voltage supply or input is indicated at l0, passing through the customary tuned inductive resistance, and being connected as by the wire l I to the plate of the tube A, and from the cathode of the tube A to the grid of tube 4 by the wire Ila, and directly to the grid of the tube 5 by the wire I3. The plate of tube 4 is connected directly by the wire I4 to the grid of tube 6, and likewise the plate of the tube 5 is directly ccnnected by wire I5 to the grid of the tube l;y the plates of the tubes 6 and 'I being connected by wires IB and II to the center tapped audio frequency choke coil I 8, across which the output I9 is taken.

The resistor R5 is attached to the Wire 2 at one end and at the opposite end to the lament of the 250 tubes 6 and l. This resistor R5 is permanently adjusted to the proper value so that the plate current flowing in the 250 tubes will cause a drop of just 274.6 volts across R5, thus leaving 450 volts across the filament and plate of the 250 tubes, which is the proper plate voltage for same.

At 20 is illustrated a small condenser connected to the wires IIa and I3 for bypassing the high frequency carrier currents in the output of the rectier A.

R8, R9, RI 0, and RI I represent a resistance between the wires IIa and I3 through which the rectified signal currents are forced to flow, thus building up a voltage across this resistance which will be applied to the grids of tubes 4 and 5.

The resistance R6 is connected by the wire 22 to the point 2I at the junction of resistors R3 and R4 of the plate voltage supply resistor, which point is 365.2 volts negative with respect to the positive side of the voltage supply, and connected by the wire 23 to the wire I4.

The resistance R1 is connected by the wire 24 to the wire 23, and by the wire 25 to the junction of the resistors R8 and R9.

The resistance R6 forms what is commonly known as the plate or output impedance of tube 4 and across which the signal voltage amplified by the tube 4 appears; this resistance R6 being common to both the plate circuit of tube 4 and grid circuit of tube 6. Resistance R'I represents a high resistance used in a novel manner and connected as previously described for the purpose of providing an additional path whereby both steady and varying currents in R6 can flow and across which progressively decreasing potentials may be had, finally decreasing to a level with or lower than the potential of the grid or other element if desired, in which case the currents can be caused to flow through a resistor common to the grid or other circuit before returning to the battery, or voltage source. By this means any desired action may be obtained for instance direct current voltages impressed on the grids may be canceled out, or a regenerative action may be obtained by utilizing such potentials to assist voltages impressed on the grids. These actions are hereinafter more fully explained.

The combination of plate current as indicated in Figure 1 flowing in the 224 tube 4 and the current through resistances R'I and R8 in series, flowing in R6, will cause a voltage drop across RB of 164.8 volts. As the grids of the 250 tubes should be operated at volts negative with respect to their laments, it is necessary to connect the lower end of R6 by wire 22 to a point having a potential of 164.8 minus 80 volts, or 84.8 volts more positive than the potential level of the laments of the 250 tubes.

If the cathode of the tube 4 is connected at the point indicated at 26 there will be an impressed plate voltage of 338.8 volts, and subtracting the drop across resistor R6, an effective voltage of 174 volts is impressed on the plate of the 224 tube, which is the amount indicated as proper by curve taken of the tube.

Thus the filament and plate returns or" the various tubes used are connected to points along a voltage supply resistor, or battery if desired, at such points that the plate voltages are correct, and so that the grid end of plate resistor (R6 in this case) is negative with respect to the larnent of the 250 tube by an amount that is proper for that tube or other proper values Where other tubes are used.

The screen grid voltage is supplied by the Wire 30 to the tube 4 by virtue of the drop across resistance RI.

Grid voltage to the tube 4 is applied as follows: A voltage of minus 20.6 volts is impressed between filament and grid of tube by the drop across R. This is too great a negative potential for this tube so the drop across resistor R8 due to currents which iiow in resistors R6, R1, and R8 in series is used to oppose this excessive nega tive voltage. The drop across R8 is shown as iix'ed at 19.4 volts and the current ilows in a direction such that this 19.4 volts opposes the 20.6 volts across R; both voltages being impressed between grid and lament of tube 4. Thus there is an effective negative voltage of 20.6 minus 19.4 or 1.2 volts applied to the grid of tube 4, which is proper.

The rectifier A is in series with the resistors R8, R9, RIU, and RI I, and also in series with the signal voltage supply, thus there will be a signal voltage in resistors R8, R9, RID, and RII, which is desired; however there will also be a direct current component across R8, R9, RIU, and RII which is not desired and which is balanced out in the following manner to prevent it from unbalancing the two sides of the amplifier.

Assume that a direct current flows through resistors R8, R9, RIU, and RII in such a direction as to cause the grid of the tube 4 to be 1 volt more positive. A plate current grid voltage curve taken of the tube 4 indicates an increase of .38 milliampere in plate current per grid volt applied under the conditions shown and described in Figure 1. Assuming this increase could occur in the above circuit, it would cause an additional drop across resistor R6 of 76 volts, therefore an equal decrease will be found across R'I and R8 in series. (Resistor Ris also in series with R1 and R8 and the tubes 4 but the same condition is occurring on the opposite side of the push pull I circuit but in an opposite direction and the two currents Will cancel each other out through R, thus there will not be an effective drop across R due to these changes being described.) A decrease of '76 volts across R'I and R8 would cause a decrease of current in these resistors of .076 milliampere. This decrease in current in R8 would cause a decrease of '7.6 volts across R8 and as the drop across R8 is utilized to oppose the excessive negative potential being applied to grid of the tube 4, a '7.6 volt greater negative potential is impressed on the grid than was had before the 1 volt positive potential was impressed, thus a large decrease opposes a small increase, tending to balance the actual grid voltage at some small frac-- tion of the 1 volt impressed. 'I'his fraction depends mainly on the relationship between the resistors R'I and R8 and the amplification cone stant of the tube, thus stabilizing the circuit in so far as impressed direct current voltages are concerned. A large condenser C is connected across R8 to prevent a changing signal current from building up a counter voltage across R8, permitting the signal voltage to be impressed on grids and progressing through the amplifier to the output, but blocking any direct current changes from progressing through the. amplier.

Steady plate current varies a small amount in different tubes of the same kind and should another 224 tube bev used which draws a slightly higher plate current the same effect occurs in that the drop across R6 will be greater and the drop across R1 and R8 less, causing a slightly more negative voltage to be applied to the grid, thus inherently tending to keep current in plate circuit constant.

As an example of the above action we can assume an increase of 1 volt across grid filament of the 224 tube and also assume an amplication of 90. This 1 volt across grid lament would be, if it were possible, amplied, so that an increase of 90 volts would appear across R6 and the same decrease across R1 and R8. It may be assumed for example that theA resistance of R8 is 115 of R1 plus R8, therefore 116 of this 90 volts or 9 volts would appear across R8. If this 9 volts did appear across R8 the potential would not be the 1 volt positive but an 8 volt negative potential on the grid, and with an 8 volt negative potential on the grid the 90 volts increase across R6 which it was assumed above would be due to the original 1 volt positive 'potential impressed on the grid, could not be obtained.

To indicate about what the actual effective increase on the grid due to the l volt impressed would be, start with an increase of 5 of a volt on the grid. T16 of a volt if amplified 90 times would appear across resistor R6 and also across resistors R1 and R8 as 9 volts, and R8 being 116 of R1 plus R8, we would iind le of the 9 volts, or .9 volt, across R8. Thus if 1 Volt were impressed on the grid, it would require only 116 of this volt to support .9 volt across R8 to cancel out the balance of the 1 volt impressed. Thus an impressed direct current voltage is reduced to 116 of its original value due to the action through the circuit.

For convenience and simplicity the action thro-ugh one side of the push pull amplifier is described, but it will be perfectly obvious that the same action would obtain on the opposite side under the same conditions, the same values and circuit constants prevailing on both sides of the amplifier.

' The action on opposite sides of the amplifier will however be 180 degrees out of phase which is desired and is well understood to be the case in a push pull circuit.

Referring now specifically to Figure 2, which represents a method of connecting a three element or grid bias detector to one side of my improved circuit and the use of a phase inverter tube for impressing the signal on the opposite side of the push pull circuit in such a manner that the currents in the two sides will be 180 degrees out of phase.

In this circuit 50 represents the voltage supply source, which, as in the modication disclosed in Figure 1, can be any suitable direct current source of high voltage. The voltage source is connected by the wires l and 52 to the plate voltage supply resistors R20, R21, R22, R23, R24, and R25, and by the wire 52 to the center tap of the output audio frequency choke coil.

53 represents a screenk grid 224 tube operated as a detector; 54 represents a screen grid 224 tube operated as a phase inverter tube, while 55 and 56 represent 210 tubes, and 51 and 58 represent 250 tubes employed in the circuit. The input is indicated at 59 and the output at 60.

A` novel feature of this circuit resides in the installation of a screen grid tube 53 as a detector, the lament of which is directly coupled With the iilament of the tube 54 and heated by the same transformer 6l. The cathode 62 of tube 53 is connected to a point indicated 4at 63 along the main plate voltage supply resistor but through the resistor R64, while the cathode 65 of tube 54 is connected through the resistor R66 to the same point 63. The screen grid returns of these latter tubes are connected at 61 to the plate voltage supply resistor at the juncture of R20 and RZI. A condenser 68 is connected be tween the plate and cathode of tube 53 for bypassing high frequency'carrier currents in the output of the tube. The grid of tube 54 is connected by the Wire 69 to the resistor R10 at a point 98, the object of which will be hereinafter described. The opposite end of resistor R is connected to the grid end of the resistor R1l. The wire 12 connects the lower end of resistor R10 to the plate voltage supp-ly at the point 63. The wire 13 is connected to the resistor R1I and to the resistor R14 which is also connected to the plate voltage resistor at the juncture of R22 and R23. At this same point the resistor R is connected, the opposite end of which is connected by the wire 16 to and through the resistor R11 and by the Wire 18 to the resistor R19, the opposite end of which is connected by the Wire 80 to the point 63. Resistor R15 is connected by the Wire 8| to the resistor R82, the opposite end of which is connected to the grid end of resistor R83. The opposite end of R83 is connected by the wire 84 to the plate Voltage supply at the juncture of R and R25. From said juncture the wire 85 leads to the resistor R86, the grid end of which is connected to resistor R81, and the opposite end of the latter is connected by the Wire 88 to the resistor R14. As is obvious all tubes are directly connected in series as in Figure l, the last ones 51 and 58 being connected in the'usual manner to the output impedance, and the input is connected between the grid of tube 53 and point 63.

The grid bias of tube 53 is obtained by the voltage drop across resistor R64 due tothe plate and screen grid currents in said tube which flow through R64 in a direction to hold the cathode of the tube positive, withrespect to the grid, at the proper potential for good detection. The degree of steady plate current in said tube is dependent upon ,its grid bias, but since the grid bias is obtained from the flow of plate and screen grid currents in the tube through resistance R64, the resistance R64 becomes the controlling factor in determining the degree of steady plate current. Condensers 80 and 9| are used to bypass audio frequency currents' around R64 and R to prevent signal voltages from being attenuated.

The grid of tube 5 4, as previously described, is connected to the resistor R10 at the point 90. The signal voltage across point 90 and point 63 will thus be impressed on grid of tube 54; point 90 being determined such that'this voltage will be an amount which when amplied by tube 54 will appear across resistor R11 as an amount equal but opposite in phase to the voltage across R11. The potential 'of point 90 being thus determined it will be .necessary to regulate the value of resistor R66 so that the voltage drop across R66 due to the plate and screen grid currents in tube 54 with no signal impressed will be 1.2 volts, (or an amount such that is proper for the grid oi the tube voperated as an amplifier) greater than the drop between point 90 and point 63 when no signal is impressed, in which event the proper voltage will be applied to grid of tube 54.

There is also shown in this circuit a novel method of obtaining a regenerative feed back, this being obtained by causing the signal current in R82 to ow through part of resistor R15, and as these signalcurrents in resistor R82 are in phase with signal currents in resistors R11 and R15, any voltage across R15 due to these feed back currents will be impressed between grid and lament of tube 56 in phase with voltage across R11, thus obtaining a regenerative feed back from the plate circuit of tube 55 to the'grid circuit of tube 56. The same action occurs by the regenerative feed back from the plate circuit of tube 56 to the grid circuit of tube 55 due to resistor R01 being connected to resistor R14. The wires 8| and 88, if desired, could be reversed, connecting wire 8| to R14 and wire 88 to R15 and by placing large condensers across R14 and R15 a greater stability to slow voltage changes, identical with the stability obtained in Figure 1, is obtained, due to the fact that the currents in R1 are caused to flow through R8. The eiTect in this case would be to tend to keep steady plate currents in tubes 55 and 56 constant, permitting values of R83 and R86 to be varied somewhat to cause equal amplication of the two sides of the circuit without changing the bias on the tubes 51 and 5,8. This is desirable for a number of obvious and well known reasons.

The resistors R83, R86, R1I and R11 operate, in all other respects, similar to the corresponding resistors in the modied circuit described in Figure 1.

The wire 80 could be connected to the cathode end of R64 instead of to the point 63, making R64 a part of R19, the additional currents in R19 assisting the screen grid and plate currents of tube 53 to stabilize the circuit against slow voltage changes.

Reference is now particularly made to the showing in Figure 3 of the drawings, wherein the basic circuit employed is identical to that described and illustrated in Figures 1 and 2, and comprises a battery or other source of supply I connected by the wires IOI and |02 to the main voltage supply resistor R|03, RI04, RI05, and RIOS, and center tap of output audio frequency choke coil. The input is indicated at |01 and the output at |08, being in all respects identical to that shown in Figure 1. B represents a two element rectier used for the same purpose as that shown at A in Figure 1. A wire |09 connects the rectifier B to the grid of tube IIO, the plate of which is connected by wire I I to the grid of tube I|2, and the plate of the latter is connected by wire I I3 to one side of the output impedance. The wire |I4 connects the other side of the input tuned transformer to the grid of tube II5, the plate of which is connected by the wire II6 to the grid of tube II1, and the plate of the latter is connected by wire I I 8 to the opposite side of the output impedance. A 'condenser I|9 as commonly used for bypassing the high frequency component of the rectied current is connected to the wires |09 and II4. The resistor RI20 is also connected across the wires |09 and I I4 through which the audio frequency component of the rectied current will flow for the purpose of building up a signal voltage to be impressed upon the grids of tubes |I0 and II5. At the center of resistor R|20 is connected the Wire I2| which is adjustably 'connected to the main voltage supply resistor at the juncture of RI03 and RI04, this being for the purpose of adjusting the grids of tubes ||0 and ||5 at the proper negative voltage with respect to the cathodes of. said tubes. A resistor R|22 is connected to the wire vI0I and to the filament-of tubes ||2 and ||1. The value of this resistor is adjusted so that the plate current owing therethrough willcause a voltage drop, which drop, subtracted from theytotalv supply voltage, will leave the proper voltage applied to the plates of tubes ||2 and. I I1. The cathodes |24 and |25 are connected together through the resistors R I 26 and R|21 and to the wire |0I at point |33, and the large condensers |28 and |29 are placed across RI26 and R|21. The action of the combination of these resistors and condensers is to provide a. grid bias to tubes I I0 and I'I5 and at the same time to permit the detected signal to be applied directly to the grids of tubes I|0 and II5. 'Ihese two actions are accomplished as follows:

The steady plate and grid currents owing in tubes ||0 and I|5 causes voltage drops across R|26 and R|21 respectively, this drop depending on the value of resistors R|26 and RI21 and the Value of the current. The value of the current when no signal is impressed will be a constant depending on circuit adjustments, the value oi.' RI26 and R|21 being adjusted at approximately 20,000 ohms for reasons hereinafter explained.

.The value of the plate and screen grid currents in each tube I0 and I I5 with one practical circuit adjustment would be approximately ,65 milliampere. This current flowing through the 20,000 ohms resistor RI26 or R|21 would cause a voltage drop of 13 volts across RI26 and also across RI21. This would hold the cathodes of tubes I I0 and I| at 13 volts positive with respect to grids of same tubes, whereas there should be approximately 1.2 volts potential difference between cathodes and grids. Wire I2I completing the circuit between the cathodes and grids of tubes I I0 and I I5 is returned to a point at the juncture of RI 03 and R|04, which point should be 11.8 volts more positive than the point |33, this adjustment leaving 13 minus 11.8 or 1.2 volts negative bias on grids of tubes ||0 and I|5. As long as no voltage is impressed across points |30 and I3| and other conditions remain 'constant these grid voltage adjustments will remain the same.

Should a steady voltage be applied across points |30 and I3I such that point |30 for example is some amount positive with respect to point I 3 I, there would be an increase in current in tube I|0 and a decrease in current in tube II5. 'I'his Voltage across points |30 and I3I will be divided equally between the grid and cathode of tube I I 0 and the grid and cathode of tube I|5.

The increase in current in tube I|0 will cause an increase in voltage to appear across R|26 and the decrease in current in tube I I5 will cause a decrease in voltage to appear across R|21.

This increase in voltage across RI26 will be impressed between cathode and grid of tube I I0 and will add to the original negative 1.2 Volts impressed and the decrease in voltage across R|21 will be impressed across the cathode and grid of tube ||5 and will subtract from the original 1.22 volts, and it is found that the voltage impressed across points |30 and I3| will be opposed by thevoltage difference across R|26 and R|21 due to this impressed voltage.

This voltage built up across RI 26 and R|21 will be larger, the larger the values of RI26 and RI21, therefore values of RI26 and R|21 should be chosenfor maximum practical results in the stabilization of the circuit against direct current voltage changes across resistor RI2D, the value of 20,000 ohms, previously assigned, being about proper for this particular tube.

As was more fully described in the remarks applicable to Figure 1, this blocking out or attenuating of direct current voltage changes will permit the detected signal currents to be applied directly to the grids of tubes H0 and H5 without the customary use of reactances to prevent improper voltages being applied to the grids; this being the object in View in this case and forms one of the novel features of the invention. The condensers |28 and 129 prevent the signal currents from building up a voltage across RI26 and RI21 and thereby blocking out the signal voltage change in the manner that the direct current and slow voltage changes do.

'I'here is also shown in Figure 3 a regenerative feed back as applied to the screen grids of tubes H0 and II5, the action of which is identical to that described in Figure 2 as applied to the control grid of tubes 55 and 55. This regeneration could be applied to an auxiliary control grid if such tubes were available, and the operation of the circuit otherwise would be identical to that illustrated and described in the other two views.

In the drawings and description, particular types of tubes have been referred to and certain adjustments which are to be made to permit these tubes to function properly. It is not my object to limit the application of the principle of the circuit to these particular tubes, nor to the particular adjustments necessary for operation of these tubes. These tubes were specied merely to disclose a clear description of the principal features of the circuit, and any other suitable tubes can be used when proper adjust- Ament of circuit constants are made which are suitable to the type of tube used.

Neither is it my object to limit the circuit to .the amplification of the output of a grid bias and two element detectors, nor to the amplification of any certain frequency band. Any suitable signal source can be used and with proper adjustments any direct current voltages Yor varying voltages of any frequency can be supplied to the input and amplified through the circuit, the output of which can be used for any purpose to which it is applicable, neither is it ,my object to limit the application of the principle to push pull circuits.

Furthermore it is not the intention to limit the use of resistances as loads on the tubes, as it is clear that inductive reactances could be used is a diagrammatic representation of that porthat would equal the drops between the negation of Figure 1 which acts to permit the rectied output of a two element detector to be applied direct 4to the push pull circuit by stabilizing the circuit against slow Voltage changes. The same reference characters are used in Fig. 4 to identify corresponding parts as used in Figure 1.

The battery is represented at I, and represents rthat portion of the battery in Figure 1 tive side thereof to the junction of R3 and R4,

and is connected by wire 2 to point X of the network and by wire 3 to point Y of the network. Resistors RI, R2, and R3,`are joined in series, and connected between points Y and point S of the network. Resistor R is connected between points S and point X of the network. Resistor RI is connected between points Y and P of the network, and resistors R1 and RilA are connected in series between the points P and X, while resistor R21 is connected between points H and Y of the network. Resistors R28 and RII are connected in series between points H and X, and RIG is connected at the juncture of R28 and RI l and the opposite end to the grid of tube 5. Resistor R9 is connected to the juncture of R1 and R8 and the opposite end to grid of Vtube 4. Point P of network is connected by wire i4 to the piate of tube 4, and point H is connected to plate of tube 5 by wire I5. The filament of tube 4 is connected to point S by wire I1, and the filament of tube 5 is connected by wire i8 to wire I1. Screen grids are omitted to simplify the drawings. The output is numbered 5 and 1 to indicate that output terminal 6 would connect the grid of tube I5` and output terminal 1 would connect to grid of tube 1. Arrows indicate the direction of the currents when no signal is impressed across the input.

As indicated in Figure 4 the fundamental stabilizing circuit forms an unbalanced double bridge, two of the arms of the bridge being common to both bridges.

The rst bridge consists of arm R and arm RI, R2, and R3, which form one branch of the lfirst bridge, the second branch consisting of arm RS and arm R1 and R8 in series. Second bridge consists of the arm R and'arm RI, R2 and R3,

which form one branch of the second bridge,

'the second branch consisting of arm R21 and arm R28 and RII in series.

nected across R8 and across RII, are here replaced by a large condenser connected between the junction of RI I and R28 and the junction of R1. Yand R8.

ence in voltage drop across R Yand the voltage drop across R8 and the grid bias of tube 5 is Signal voltdescription of Figure 1.

Figure 4 is presented to more clearly illustrate,

diagrammatically, the action of the combination,kw and as the characteristics of bridges are well un" derstood, it. willV be clear that if R6 and R21 are equalgand R1 and R28 are equal, and that' R8 and RI I are equal and the current in tubes 4 and ,.5 the same, then there will beno voltage difference found. between terminals 6 and 1. With the values of resistors as given in Figure 1 both 40 Large condensers C, shown in Figure 1 as con- Grid bias for tube 4 is obtained by the differ-:A5

bridges are in an unbalanced condition and both bridges are equally unbalanced.

rent in the tube 5 would tend todecrease if there were no counter action to prevent this.

As the tube 4 is in series with RB and the tube 5 is in series with R21, a-greater voltage drop would appear across R6 and a lesser drop across.y R21, causing a difference in potential across terminals Gand 1. R1 and R8 are in series with R5 and the battery, and a smaller drop would be measured across R1 and R8 due to the larger drop across R6.

R28 and RII are in series with R21 and the battery, and a larger drop would be measured across R28 and RII due to the smaller drop across R21.

The point of junction between R1 and R8 would be at a lower potential and the point of junction between RII and R28 would be at a higher potential than was the case before the voltage was applied across the input, thus the action of the bridge is to build up a difference in potential across the junction of R8 and R1 and the junction of RII and R28 which will oppose any difference of potential applied across the input; however this will be the action only for comparatively slow rates of change in potential differences applied to the input terminals. Where comparatively fast varying diierences in potentials are applied across the input terminals the condenser C will not permit a change in potential between the junction of R1 and R8 and the junction of RI I and R28 and the fast varying potentials will therefore cause a difference in unbalance between the two bridges and an amplified duplicate of the changes across the input will be found across the output terminals 6 and 1.

Thus a portion of the arm consisting of R1 and R8 and the arm consisting of R28 and RII become the controlling factors governing the amount of current that can be passed by the tubes 4 and 5, tending to keep the currents constant when a slow varying difference in potential is applied to the input terminals, but permitting the currents to vary in step with any fast varying potential differences applied to the input terminals.

Should a small change in values of R6 or R21, or small changes in tube currents occur, the same action would obtain tending to hold the currents through tubes constant.

R and R8 and RI I are adjusted so that the grid bias with no signal impressed across input is proper for the type of tubes used.

R28, if desired, could be connected to R8 and R1 connected to RII and condenser C eliminated and thus obtain a regenerative action rather than a degenerative action, at all frequencies, or if desired condenser C could be retained, in which case the regenerative action would obtain for slow varying potentialsonly.

Having thus described my invention, what I claim and desire to secure by Letters Patent, is:

l. In a direct coupled radio receiving circuit, comprising resistance in the plate circuits, a two element rectier, a resistance in series with the rectifier, and means for bypassing a portion of said latter resistance for cancellingv out the direct current component in the rectied current.

2. An amplifier for radio receiving circuits including vacuum tubes directly connected in series, the output'circuitof one tube being connected to the input circuit of the succeeding tube,

, and a plate voltage supply and a plurality of rewir sis'tors connected to the common plate and grid connections providing a plurality of separate paths for the signal and other currents in the output of said tubes and across which plate potentials progressively decrease, a portion lof a separate path being. common to a preceding Vinput circuit.

3. In combination with a radio receiving'circuit, of an audio amplifier including a plurality of vacuum tubes directly coupled, the output circuit of one tube being connected to the input circuit of the succeeding tube, and a plurality of resistors having common connections to said connected input and output circuits, at least one of said resistances being connected to bridge a portion of the input circuit of said first tube for the purpose of providing audio feed back.

4. In combination with a radio receiver circuit, an audio amplier including a plurality of vacuum tubes arranged in a series cI" push-pull stages, the output circuit of each tube in one stage being directly connected to the input circuit of a corresponding tube in a succeeding stage, and resistance coupling means for providing regenerative feed back between the stages.

5. The combination with a receiving circuit of an amplifier therefor characterized by having the output of one tube directly connected to the input of the following tube, a plurality of resistors forming a portion of a bridge circuit, each resistor having one end connected in common with each other and to the common plate and grid circuit, one of said resistors having its other end connected to a source of high potential in said circuit, and another of said resistors having its other end connected to the bridge circuit of a preceding tube.

6. In a radio receiving circuit in combination, an amplifier including a plurality of vacuum tubes connected in cascade, the plate of one tube being directly connected to the grid of the succeeding tube, said connection having connected thereto the common ends of a plurality of resistances, one of said resistances having its other end connected to the input of a preceding stage, and another of said resistances having its other end connected to a source of plate supply.

'7. The combination with a receiving circuit, of an amplifier including a plurality of vacuum tubes directly coupled, the plate of one tube being directly connected tc a grid of the succeeding tube, and a plurality of resistors one end of each being connected in common with said plate and said grid, one of said resistors having its other end connected to a control grid of a preceding tube for the purpose of providing feed back.

8. A radio receiving circuit including a plurality of tubes arranged in a series of push-pull stages, interstage conductors each directly connecting the output of a tube in one stage to the input of a corresponding tube in the succeeding stage, and a plurality of groups of resistors each having one end connected in common with one of said conductors, one resistor in each group having its other end connected to a control grid of a tube of the opposite phase.

9. In a radio receiving circuit, a source of audio frequency current, an amplifier including a vacuum tube, and non-reactive connections between saidsource and said tube, a resistance in series with said source, a'capacitor by-passing a. portion of said resistance, a plurality of parallel resistors connected in common to the plate circuit of said tube, and means for providing direct current feed back to said source via one of said parallel resistors.

10. Ina radio receiving circuit for radio signals, an amplifier including thermionic tubes in pushpull stages connected in series, one side of a pushpull stage being energized by an audio frequency current source and the other side of said stage being energized by a tube arranged as a phase inverter, and a plurality of parallel resistors one of which comprises the grid impedance for the tube energized by the source, a portion of the signal voltage across another of said resistors being applied to a control grid of the inverter.

11. A radio amplifier including a plurality of tubes arranged in a series of push-pull stages, the outputs of the tubes in one stage being directly connected to the inputs of corresponding tubes in the succeeding stage, and a plurality of resistors coupling said tubes and some of which provide regenerative feedback between the stages.

12. In a radio amplifying circuit, a rectifier, an amplier including a vacuum tube, non-reactive connections between said rectifier and said tube, a resistance in series with said rectifier, a capacitor by-passing at least a portion of said resistance, a plurality of parallel resistors connected in common to the plate circuit of said tube, and means for providing direct current feedback to said rectifier circuit via one of said parallel resistors.

13. In a direct coupled amplier system, a plurality of resistors interconnected to form a bridge circuit, a thermionic tube having its plate connected to one corner of said bridge circuit, its cathode connected to an opposite corner of said bridge circuit, and its grid connected to one arm of said bridge circuit and adapted to control currents in said bridge circuit by means of the amplifying effect of said tube.

14. In a direct coupled amplifying system, a plurality of resistors interconnected to form an unbalanced bridge circuit, a thermionic tube having its plate connected to one corner of said bridge circuit and having its cathode connected to an opposite corner of said bridge circuit, and a grid of said tube connected to one arm of said bridge circuit and adapted to control to prevent any further unbalancing of direct current in said bridge circuit, by means of the amplifying effect of the tube.

15. In a direct coupled amplifying system, a stage comprised of a pair of thermionic tubes connected in phase opposition to each other, a plurality of resistors having one end thereof connected in common to each other and connected to the plate of one of said tubes, a second plurality of resistors each having one end thereof connected in common to each other and connected to the plate of the other of said tubes, the other end of one resistor in each of said pluralities being connected to a source of plate potential, means connecting the other end of another resistor in each of the said pluralities to a source of potential less in value than that of said first source, means for impressing a modulated frequency on the grid of said rst tube, and means for impressing a voltage from the output of said first tube upon the grid of said second tube, said last means being connected to a point, on one of said resistors associated with the plate of said first tube, at which the intensity of said last voltage when amplified by said second tube is substantially equal to the plate voltage of said first tube.

GUY I-I. PARIS. 

